diff --git a/.gitignore b/.gitignore
index 42f590f1..bf07040e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,6 @@
 *.pyc
+web/game.zip
+web/game_version.txt
 screenshots/*.png
 saves/*/*.json
 saves/*/rooms/*.json
diff --git a/src/mapimage/mapImageGenerator.py b/src/mapimage/mapImageGenerator.py
index 807c60bf..5edfc8f0 100644
--- a/src/mapimage/mapImageGenerator.py
+++ b/src/mapimage/mapImageGenerator.py
@@ -60,7 +60,11 @@ def mapImageExists(self):
     def getExistingMapImage(self):
         mapImagePath = self.getMapImagePath()
         _logger.debug("loading existing map image", path=mapImagePath)
-        return Image.open(mapImagePath)
+        try:
+            return Image.open(mapImagePath)
+        except Exception:
+            _logger.warning("map image unreadable, recreating", path=mapImagePath)
+            return self.createNewMapImage()
 
     def createNewMapImage(self):
         _logger.debug("creating new map image")
diff --git a/web/build_zip.py b/web/build_zip.py
index 5dd13990..2ab3c55a 100644
--- a/web/build_zip.py
+++ b/web/build_zip.py
@@ -3,7 +3,12 @@
 
 Bundles the Python source tree, schemas, and config into a single zip that
 the browser's Pyodide Worker downloads and unpacks into its virtual filesystem.
+
+Also writes web/game_version.txt containing the SHA-256 of the zip so the
+Worker can request game.zip?v=<hash> — a content-addressed URL that forces
+the browser to fetch a new zip whenever the source changes.
 """
+import hashlib
 import os
 import zipfile
 
@@ -26,4 +31,9 @@
         if os.path.exists(_web_file):
             z.write(_web_file, _web_file)
 
-print("Built web/game.zip")
+with open("web/game.zip", "rb") as _f:
+    _digest = hashlib.sha256(_f.read()).hexdigest()
+with open("web/game_version.txt", "w") as _f:
+    _f.write(_digest)
+
+print(f"Built web/game.zip ({_digest[:12]})")
diff --git a/web/game-worker.js b/web/game-worker.js
index 7504600f..829db995 100644
--- a/web/game-worker.js
+++ b/web/game-worker.js
@@ -178,7 +178,16 @@ self.onmessage = async (e) => {
 
         self.postMessage({ type: 'status', msg: 'Downloading game…' });
 
-        const resp = await fetch('/web/game.zip');
+        // Fetch the content-hash written by build_zip.py so the zip URL is
+        // unique per build. The browser may cache game.zip?v=<hash> freely;
+        // a new deploy changes the hash, forcing a fresh download.
+        let zipUrl = '/web/game.zip';
+        try {
+            const verResp = await fetch('/web/game_version.txt', { cache: 'no-store' });
+            if (verResp.ok) zipUrl += '?v=' + (await verResp.text()).trim();
+        } catch (_) { /* no version file — fall back to unversioned URL */ }
+
+        const resp = await fetch(zipUrl);
         if (!resp.ok) throw new Error(`game.zip fetch failed: ${resp.status}`);
         const buf = await resp.arrayBuffer();
         pyodide.FS.mkdir('/game');
diff --git a/web/serve.py b/web/serve.py
index b9d737fa..bc252110 100644
--- a/web/serve.py
+++ b/web/serve.py
@@ -43,6 +43,14 @@ def end_headers(self):
         self.send_header("Cross-Origin-Opener-Policy", "same-origin")
         self.send_header("Cross-Origin-Embedder-Policy", "require-corp")
         self.send_header("Cross-Origin-Resource-Policy", "same-origin")
+        path = getattr(self, "path", "") or ""
+        bare = path.split("?")[0]
+        if bare.endswith("game_version.txt"):
+            # Never cache — the Worker fetches this to get the current zip hash.
+            self.send_header("Cache-Control", "no-store")
+        elif any(bare.endswith(ext) for ext in (".zip", ".js")):
+            # Revalidate on every request so a new deploy is always picked up.
+            self.send_header("Cache-Control", "no-cache")
         super().end_headers()
 
     def log_message(self, *args):